(1) Field of the Invention
The present invention relates to a display device, and in particular, a display device having a polarizing plate.
(2) Description of the Related Art
Liquid crystal display devices (panels) are formed of a pair of substrates provided so as to face each other and sandwich liquid crystal, and polarizing plates pasted to the respective substrates on the side opposite to the liquid crystal. An amount of light that transmits through the polarizing plates can be changed for the display by controlling the molecules of the liquid crystal by means of an electrical field. The polarizing plates are usually provided so that the respective absorption axes cross at a right angle.
In this case, the respective polarizing plates are formed by layering at least a protective film (hereinafter referred to as an inside protective film), a polarizing film (also referred to as polarizer or polarizer layer), and a protective film (hereinafter referred to as outside protective film) on the above described substrate. The polarizing film in itself has polarizing properties, and when an inside protective film and an outside protective film are provided, the durability of the polarizing film and the resistance against scratching are higher.
FIG. 2 is an exploded perspective diagram showing a polarizing plate (hereinafter referred to as upper side polarizing plate) POL2 pasted to the surface of a conventional liquid crystal display panel PNL on the viewer side and a polarizing plate (hereinafter referred to as lower side polarizing plate) POL1 pasted to the surface on the side opposite to the viewer. The upper side polarizing plate POL2 is pasted to the liquid crystal display panel PNL and formed by layering an inside protective film PSI2, a polarizing film PLF2 and an outside protective film PSO2 with adhesive layers (not shown) in between on the liquid crystal display panel PNL. Likewise, the lower side polarizing plate POL1 is pasted to the liquid crystal display panel PNL and formed by layering an inside protective film PSI1, a polarizing film PLF1 and an outside protective film PSO1 with adhesive layers (not shown) in between on the liquid crystal display panel PNL. In this case, the respective expansion axes EA of the inside protective film PSI2 and the outside protective film PSO2 are directed in the direction of the expansion axis EA of the polarizing film PLF2 (all the axes are directed in the same direction) in the upper side polarizing plate POL2 while the respective expansion axes EA of the inside protective film PSI1 and the outside protective film PSO1 are directed in the direction of the expansion axis EA of the polarizing film PLF1 (all the axes are directed in the same direction) in the lower side polarizing plate POL1. The configuration shown in FIG. 3, for example, is known as a configuration of a conventional polarizing plate other than that in FIG. 2 (see JP 2007-65191A). FIG. 3 corresponds to FIG. 2.
In FIG. 3, the configuration is different from that in FIG. 2 in that the inside protective film of the upper side polarizing plate POL2 is arranged so that the expansion axis EA of the inside protective film crosses the expansion axis EA of the polarizing film PLF2 in the upper side polarizing plate POL2 at an angle of 45° or 135° while the inside protective film of the lower side polarizing plate POL1 is arranged so that the expansion axis EA of the inside protective film crosses the expansion axis EA of the polarizing film in the lower polarizing plate POL1 at an angle of 45° or 135° (see θ2 in FIG. 3). Though JP 2007-651919A does not directly describe this, the respective expansion axes of the polarizing film (polarizer layer) and the inside protective layer can be interpreted so as to cross at an angle of 45° or 135° from the description that the protective layer (inside protective layer) of the polarizing film on the liquid crystal display panel side is provided with birefringence so as to optically function.
Here, FIGS. 2 and 3 correspond to FIG. 1 showing the configuration according to an embodiment of the present invention. Therefore, the above description merely relates to the disadvantages in the configurations shown in FIGS. 2 and 3, and the other parts of the configuration are described in detail in reference to FIG. 1.
The documents that relate to the present invention in addition to the prior art shown in FIG. 3 are JP 2003-207620A and JP 1997-325216A, for example.
JP 2003-207620A describes that a transparent protective film is formed on at least one side of a polarizing film, and the slow axis of the above described transparent protective film and the absorption axis of the above described polarizing film form an angle of 10° or greater and less than 90°. Here, in the case where transparent protective films are provided on both sides of the polarizing film, the slow axis of the outside protective film and the slow axis of the inside protective film are assumed to be in the same direction.
JP 1997-325216A describes a liquid crystal display device in which transparent protective films are provided on both sides of a polarizing film, the transparent protective film formed on one side of the polarizing film exhibits birefringence with an in-plane phase difference 50 nm to 200 nm, and the slow axis of the transparent protective film having this birefringence is parallel or perpendicular to the transmission axis of the polarizing film. Here, the slow axis of the outside protective film and the slow axis of the inside protective film are in the same direction.